The wax/contact paper?
The process is very similar between the two so I'll just explain and then comment after. You're basically gonna print out your design and trace it onto the paper. Your gonna cut the inside of the design out basically making a big stencil. Attach that to the shirt and paint it in.
Contact paper is really cool because when you iron it it will adhere to the shirt due to the film on the one side. When you pull it off it doesn't leave residue. Contact paper has a sticky side but when I used it also didn't leave a residue.
Now you're doing John but I'm not sure which version, normal or God Tier. If normal you've got that ghost/worm thing so you're gonna have to decide if you want to carefully place the eye slits and fill in later or just paint over the green. Painting over is gonna give you more layers though. Also, you would want to figure out when you're cutting if you want to remove the black outline and free hand it otherwise again more layers.
I hope some of this was at least somewhat helpful and sorry if it got kinda long. Good luck on getting your stuff done.
WIP to be debuted
San Japan: Laxus Dreyar (Fairy Tail)
Alamo City Comic Con: Hawkeye (Fraction run),
Street Vigilante Red Hood